Propeller control



Jan. 2, 1951 R. E. MOORE PROPELLER CONTROL 2 Sheets-Sheet 1 Filed Deo. 25, 1946 ATTORNEYS Jan, 2, 1951 R. E. MOORE 2,53538 PROPELLER CONTROL Filed Dec. 25, 1946 2 Sheets-Sheet 2 f/js A TTORNEYS Patented Jan. 2, 1951 2,536,138 PeoPELLER CONTROL Richard E, Moore,Dayton, Ohio,` assigner to General Motors Corporation, Detroit, Mich., a corporation of Delaware Application December 23, 194.6;.SerialNm *118.971

15 Claims.

This invention relates to the control of variable pitch Vpropellersy particularly those involving fluid pressure mechanism for shiftingl the blade pitch to accomplish desired ends.

One of the vobjects of the invention is to reduce the amountv of ofi-speed of a governing system by increasing` the proportionalizing rate of a control valve.

Another object of the invention is to provide a propeller control by which the propeller speeds are caused to followcloselv and quickly accelerationand deceleration ofthe driving force.

Another object of the invention -is .to `maintain the .source pressure at a fixed amount above the pressure necessitated for operating one of the pitch control functions.

A further object of the invention is to provide a fluid pressure system of the variable pressure constant-leak type that will not interfere with maximum rates of pitch change and/or flow-sensitive feathering systems.

A further object is to provide a uid pressure system and control vapparatus therefor that will maintain the required pressure against the ever present blade load tending to shift to a predetermined position.

Still yanother object of the invention. is to provide a governor controlled fluid pressurevsys.- tem of high potential, in which the-governor .be-

comes a true now governor and only throttles pressure fluid throughone port during normal opera-tion, thereby removing. all reversing flow forces from the governor va1ve,.and maintaining a constant pressure drop across the governor.

Yet another object of the invention is to provide a fluid pressure system for the control of variable pitch propellers, which system will have maximum vpressure sensitivity as well as produce an ideal constant pressure differential between source lpressure and increase pitch port pressure.

Among other objects of the invention is to provide a fluid lpressure system pf control Vfor variable pitch propellers whose .blades have high centrifugal twisting moments tending to decrease pitch.

The indicated objects and advantages are accomplished by Aproviding a pressure control unit of threeelement structure that incorporates an equal area valve operating in the nature of a pressure control valve whichis constantly vconnected with a pump source and operates to meter flow through the increased pitch port/of the governor valve and apply the pressure potential. of .that .port to .a constant-.leak valve as `2 a second element of the unit, and which operates to maintain a constant pressure diierential between the increased pitch port of the governor and apressure source. The third element of the unit,.is .a relief valve constantly exposed tothe source Ypressure for safe-guarding the system. With ythe governor'valve so organized as to maintain,. a predetermined amount of negative over.- lap at the increasedpitch port, then a predetermined ilow of hydraulic uid is delivered to oneside .of the blade torque unit and to the exit orice of .the constantfleak valve. In normal, or on speedoperatiomthe. quantative factorpef kleak land. the pressure urge .on the -one side of the .blade torque motor balances the .centrifugal moment of rotative force` on the blade tending" to decrease the. bled? pitch, by means of which, for normal oni-.speed operation, the pitchofthe blade .isheld substantially fixed for operation at the speeds selected by the governor valve.

In the drawings:

Fig. 1 is a iluid circuit diagram illustrating the application-of .the system.

Fig. 2 isa detail view in section showing a constant leak valve forming part yof the apparatus of the instant invention, substantially asindicated by the line and arrows 2 2 of Fig. y1.

Fig. 3 lis a schematic view of a propeller mecha. nism inlcngitudinalsection and embodying the fluid circuit depicted in` Fig.A 1.

Fig. 4 is` an. enlarged detail of the port and landarrangement forthe increased pitch port Showninlig. 1.

.With particular reference to Fig. l of the drawings, vwhich .shows schematically `the hydraulic circuit, lllis a .pump or pressure developine tmeans .drawing hydraulic fluid from a reservoir thru kan intakey l2 and feeds it to a PICS- sure delivery line l, leading to the shanl;` vI8 betweenrlands landz of a governcr valve 22. .The governor valve .incorporates a .Stem .extension .24 of .the shank i6 that pvotally connects at 23 to a leverZg resting on a movable fulcrurn 3! secured to. a carriage 32, the latter being manually adjustable `as will presently appear for selecting a speed at, which the governor valve is toA control. ,The lgovernor valve unit 22 is situated for response tol centrifugal force acting toward the ltop of the sheet of drawing as `shown inFig. 1 and tending to compress a spring 31E which hclds the `lever 28 against the fulcrum 30? the valve plunger lthereby being capable ef sliding movement in a sleeve. 35 providing an increased pitch port 38 and a decreased pitch port madame@ to cooperatewith the equally 3 spaced lands I8 and 20 of the valve plunger. From the control ports 38 and 40 tubular passages 42 and 44 lead to chambers 48 and 48 respectively on opposite sides a piston element 50 contained within a cylinder 52 constituting a blade torque unit for adjusting the pitch of the propeller. The piston 50 is therefore provided with a stem 54 having a toothed rack 58 engageable with a spur 58 aflixed to the root or the blade 80 so as to rotate the blade in either direction about its pitch shifting axis 82. Considering that the propeller rotates upon an axis 64 by a shaft 68 in the direction of the arrow 88, then movement of the piston 50 toward the top of the view of Fig. 1 will so actuate the blade by rotating it around its pitch axis 82 as to increase its angle of engagement with the air stream thus increasing the blade pitch.

A branch line 'I9 leading from the pump pressure line I4 opens into a chamber '|2 forming a damping chamber '|2aand pressure regulating chamber 72b for an equal-area valve 14, a secondary connection 'I8 opening from the chambei '|2 into a pocket 'i8 into which extends a piston 80 having a flat head 82 engaged by a spring 84 contained with a chamber 88. The piston 88 is always subject to the pump pressure within the pocket I8 and is urged to the extended position illustrated by the spring 84 but is subject to depression by the pressure within pocket 'I8 until flow is established to the drain slot 88 which will relieve an excess of pressure that may occur in the pressure lines 10 and I4.

The equal area valve,vso called because the eiective actuating areas exposed to the pump or source pressure and to motivating pressure are equal and opposite as will presently appear, comprises a stem 98 having a head 92 substantially less in diameter than the bore of the chamber l2 and which is engaged by a damping washer 94 having a clearance in bore 'l2 substantially small enough t0 resist rapid motion of stem 98. Adjacent the underside of the head 92 there'is a spring 98 engaging the bottom of the chamber 12. A small axial bore 98 houses a valving portion of the stem 90, and opens into laterally extended fluid passages as will presently appear. The stem 90 is provided with a valving land |00 and a valve and guide land |02 separated by a shank portion |84 and all contained within the bore 98. An axial bore |06 extending from the lower end of the stem 90 upwardly intersects one or more cross bores |08 that open thru the shank portion |04 of the Valve so as to establish communication between an annular groove IIO about the shank between the lands |00, |02, and a pressure chamber I I2 at the bottom of the bore 88. Communicating with the annular groove II!) there is a passage ||4 that leads to a groove IIS always communicatingwth the increased pitch port 38 of the governor valve 22. A second passage ||8 communicating with the annular groove ||8 opens into a channel |20 in the porting cylinder |22 of a constant leak Y valve, flow through the passage I|8 being controlled by the land |02. The porting cylinder I 22 is disposed within a chamber |24 housing a plunger |28 having a landed stem |28 contained within a bore |30 of the cylinder |22, the bore |38 having cross passages |32 connecting it with the annular groove |20. Thus, it will be observed that the potential of pressure occurring at the increased pitch port 38 will always be applied through theconduit ||4 to the annular groove ||0, and the pressure chamber I I2, and

i under certain conditions to the cross passage ||8 and the annular groove |20. The stem |28 provides a guide land |34 spaced from a valving land |38 separated by a shank portion |38 which is characterized like the spaced lands of the equal-area valve to connect the annular groove about the shank |38 with the lower end of the valving land through a port |40 and axial bore |42 shown in sectional detail in Fig. 2. The valve stem |28 with its land |38 cooperates with cross passages |32 to regulate the amount of hydraulic fluid moving from the passage ||8 to the chamber |44 at the lower end of the stem |28, increase of pressure in the chamber |44 tending to raise the stem such that the land |38 cuts oi the ilow thru the ports |32, and being resisted by a spring |48 contained within an exhaust chamber |48 at one end of the chamber |24. The exhaust chamber |48 is ported to the outside of the valve unit at |50 and has a cross passage |52 extendingV from the chamber |48 and opening into the bore 98 of the equal-area valve in the region of one end of the valving land |00 of the stem 90, an extension passage |54 leading from the bore 98 into the exhaust chamber 88 of the relief valve which has a port of exist |58. It will be observed that the passages |52 and |54 constitute drain passages for the equal-area valve and are controlled by the valving land |00 of the stem 90 which controls'communication of these passages with the pump line pressure thru the bore 98 opening into the chamber '|2.

Briefly, variation of pressure at the increased pitch port 38 and groove ||6 of the governor 22 is applied to the conduit ||4 and to the annular groove ||0 and thence thru the opening |08 and axial bore |08 to the pressure chamber ||2. A rise or fall of pressure in I|2 alters the flexure of the spring 96 tending Vto raise the valve stem for closing the passages |52 and |54. If the pressure in chamber II2 increases, then the force applied to the valve stem 89 will assist` the spring 96 and the centrifugal force of propeller rotation in covering the orifices into the passages |52 and |54 by the land |00. When those ports or passages are closed to pressure within the chamber 12 the potential within pump line 'I0 and I4 builds up and may be so great, if no regulation is provided, as to cause a blow off of the relief valve thru the port 88. That blow off is partially prevented by the potential of pump line pressure applied thru the passage 10, chamber 12 and bore 98 to the end area of the valving land |00. The spring engagement with the head 92 of the valve is such as to provide controlled damping movement of the equal-area valve 14. The spring 98 engages the damping washer 94 which in turn engages the head or flange 92 in a loose manner, that is to say, it is only in contact therewith but is guided by the bore of the chamber 'I2 while the circular opening is of larger diameter than the diameter of the stem 90 that passes thru it. That provides for eccentricity of, or misalignment of, the bores or chambers 12 and 98 without bind- Ying or unduly resisted Ymovement of the lands |00 and |02 within the bore 98, since the flange 92 may be off center with respect to the chamber 12. The washer 94, however, is centrally disposed in the chamber 12 and its clearance with the side wall of the chamber Ycan be dimensioned to provide the rate of damping desired. A further variation inthe upward movement of the equal area valve 90 is accomplished thru the action of the constant-'leak valve |26. As heretofore stated, the pressurepotential occurring atthe `vincreased pitch lport 38 may be presentin the vannular .passage |20 and cross passages |-32 and -is Lthere controlled by the valvin'g effect ofthe land A|36 which admits that pressure potential thru the passages |40 yand |42 to the pressure chamber |44, Thus, if the pres.- sure `in |44 is increased, the land |36 will be raised somewhat to close the ports |32 which finally may stop further movement of the stern |28 wereitnot Afora carefully dimensioned bleed or-ice -|60 that 'provides va constant leak thru the lines mentioned extending from vthe in.- creased pitch port 38. As soon as land |36 moves upward or is raised, the ilow through ports |32`is reduced 4and the .pressure in |44 is reduced land that is `followed immediately by downward-.movement of land |35 to further open the yports |32 and increase the pressure `in chamber" |44, lThere results through the cooperation of -those elements a constant leak through the orifice |60. Except for conditions hereinafter stated, there Will be va continual flow of 'hydraulic fluid from the Apressure line I4 thru `the'increased pitch port 38, H6, line H4, groove `Hfll ofthe equal-area valve, and then thru the constant-leak valve to exit at the port |60. 'Since the annular channel H0 is always connected to the pressure chamber H2, the assisting effect applied ,toy the spring 56 will be under `the .control of .the constant-.leak port |60.

The 4passages |52, |54 and H8 Vare disposed in such relation to the vland |00 and l| 02 of the stem 410, that there .exists at least a slight metering .of the flow `into the passage |.8 by the time that ,the .drain through the ypassages |52 and |50 is cutoff. -When 'theorice vfrom the bore 98 into `the .passage H8 is less in area than that of the :leakorice .|60 then the rate of leak is diminished @mi fthe pressure inchamber |44 drops because ,0f the Alessened flow of fluid thereto. However vthatproduces no substantial `change in the pres- .sure line over what is A,v vrought by the diminished flow through |-8. That restriction, of course, occurs onlyvvhenthere is a considerable and sud- .,glen drop in 4pressure potential within the line 10 Athat,effects,closing of the blow off ports |52 and |54, 1T-he iline experiencing a sudden fall in pressure potential, the branch from the increase pitch ,por-t, 3 8 tothe constant-leak device is temporarily Vrestricted or perhaps entirely closed off to afford -amore rapid'recovering of the working potentialmin the pressure line. Sudden build-up of `pressure vfollowing those lconditions is amply g'fuarded against by the relief valve 80 and the `pressure control orequal-area valve which opens the orifice to 8 just as soon as the pressure in .the line .10 will accommodate vthe flow or leak Afrom port |60 and yet supply the system for governed operation.

.applying the same principles exhibited in the schematicdiagram vof Fig. 1, provides the sectional pictorial view of Fig. 3 where the elements shown in Fig. l have 'been distributed around the propeller shaft 6 6, supportedby the bearings |10, earried by an vengine nosing or gear casing |12, and from which the shalt rotatably extends to drivingly support a propeller hub |14, providing sockets |16, journalling the blades 60 fol1 pitch shi-'ifta'ble movement about their longer axes, and for revolution about the axis of the shaft 66. Roytatable -with the rshaft and hub there is a regulla-tor comprising an annular plate .|18 and a A'cover Vmember ,|80that l:,:ooperates to provide a vsired.

reservoir |82 housing vthe control apparament Fig. 1, and vhere designated as thegovernor-Mabie GV, a relief valve RV, andequal 4area valve- E Y theconstantleak valve CLVgand a pumporpres: sure creating device 0. vlThese elements are/sq mounted-upon the regulatorplate l|7113 as tQllQprerly ytake -advantage of .centrifugal force of; 9e tationwhen considering that the regulatorsuney porting and lenclosing .these .elements is rotated.. rabout vthe propeller shaft 05 as .an.axis YFluid passages extend from the pump to ,the various elementof the control apparatus in accordance with .the vprinciples expressed with respectif; Fig. 1, the pitch increase line 42 and fthefpitchde; crease line 4Q each having branches 02a .and b and 44a and b respectively Yleading to the lap: propriate chambers 46 and 489i the `two blad here shown. Instead of the rack or l.gear con: nection between the `piston and blade as :sho in Fig. l, the piston 50 4of Fig. 3 has splined en; gagement at 55a with the cylinder 52, and ,all 56h with a spindle |15 of the hub |14. Lineal movement of piston 50V rotates the'blade 60 in ts socket relative to the spindle Y1:15 by treason of the double helical splines 56a and 56h. Each of the blades is provided with a blade gear 118.4 that meshes with a master gear |86 adapted to keep the blades in track and insure that as one blade changes in pitch the other will also lchange in pitch an equal amount. Also included in Fig. 3, there is an accumulator |88 disposed axiallyof the hub v|1ll and 'providing a pressure line |90 adapted to connect into the system for use in connection with feathering `and unfeathering of the propeller blade, where that function is de.- However, since the feathering function plays no particular part in the novel control of pitch that is herein described, it is not deemed necessary to enter linto the description of blade feathering.

The control apparatus embodied within the regulator is always under control of the pilot in-so-far as the governor valve AGV ,may be set at any time to establish a, speed level at which the automatic mechanism is to control. It has been stated earlier, that the fulcrum roller 30 is mounted on a movable carriage 32 for selecting a speed at which the governor valve will control, and that is accomplished in Fig. 3 by supporting the carriage 32 between a pair of yguide ways |02 with an extension or shoe |9001? the carriage engaging a groove |96 of a control ring |98. The control ring encircles the shaft 66 and is slidable longitudinally thereof by means of high-lead control shafts v20E) threaded into the ring |98 and journaled in a flange 2020i a sleeve 2,04 maintained against rotation with the propeller, by means of a lug 20,6 engaging between bracketsor clips 208 secured to the engine nosing- |12. A ring gear 2| 0 is provided with a lever 252, and a control cable or rod 210 outside of the cover |80, engages pinlonsv 2|,6 fixed to the Vends of the control shaft 200, so that o scillation of the lever 212 rotates the screw ,Sl'laft k200 and causes axial movement of the control ring within the regulator. The flange 20,2 is

prepared with a toothed periphery 2|1 to engage a pinion2|8 that drives the pump l0. When the propeller is in operation, it Will be observed that the control" ring |98, the screw shafts 200, the sleeve 204 with its vatta :hed spur gear 2|1 are all non-rotative because of the interengagement provided by 206 and 208, which means that the propeller with .the regulator containing .the ses trol Vapparatus rotates outside of this group of elements, and is known as an adapter assembly. The pump gear 2I8 rolling over the spur 2i? effects development of pressure by the pump I within the lines I4 and 'I0 of the system which pressure is regulated by the three element pressure control valve and delivered to the governor valve. The speed of propeller rotation will be determined by the position of the fulcrum roller 30 along the length of the lever 28, since that position determines at what speed of rotation centrifug-al force acting upon the governor valve plunger thru the lever arm between the point 26 and engagement with the roller 30 will just balance the force of the spring 34 applied to the lever 28 thru the length of the arm between the point of spring pressure and point of fulcrum engagement. The relation of these working arms may be altered by actuating the arm 2I2 of the ring Vgear which in turn effects the shifting of the control ring |98 and consequently moves the carriage 32 along the ways |92 substantially as shown and described in the patents to Blanchard et al. 2,307,101 and 2,307,102.

During on-speed operation, the lands VI8 and 20 of the governor valve will so coincide with the ports 38 and 40 as to result in equal forces being applied to both sides of the piston 50 of the blade motor 52 as a consequence of which there will be no blade shift movement. In the present instance. because of the natural tendencies of the blade while in operation to seek a decreased pitch position, the particular coincidence of governor lands and ports during on-speed will involve a slight amount; of predetermined offset as designated at Y in Fig. l. That particular predetermined offset takes into account the tendency of the blade to move to `decrease pitch position, and permits an exactly balancing force of hydraulic pressure to be applied to the chamber 48 of the blade motor for opposing the built in tendency of decreased pitch shift. The off-set also maintains a continual flow from the pressure line I4 thru the passage II4 and has been described to exit atV the constant leak orifice |66. Upon the occurrence of increase in speed the governor valve moves outwardly, upward as shown in Fig. l, which increases the opening of the increased pitch port and allowssuicient pressure application to the passage 42 and the chamber 46 to move the piston 58 for increasing the pitch of the blade 60 for effecting the increase in the load placed upon the motor and consequently reflecting in a decrease of speed, in the meanwhile the chamber 48 draining thru the passages 44 and port 40 to return to the reservoir. Upon the occurrence of decrease in propeller speed, less centrifugal force is applied to the governor valve by reason of which the spring 34 moves the governor valve plunger inwardly, first, such as to completely cover the increased pitch port 38 and the decrease pitch 4U, or so as to absorb the ofi-set Y. That shift in itself so disturbs the balance of forces applied to the chambers 46 and 48 as to allow 'blade 60 to shift toward the decreased pitch position against the removal of pressure application that has been theretofore exerted in 46. If that release of opposing pressure thru the passage 42 that is afforded by means of the constant leak orifice |60 is insufficient to provide enough correction, then further inward movement of the governor valve plunger opens the port 40 to lthe pressure line and the increase pitch port 38 to drain.V In order to'restrict the rapidity of drain from thechamber 46, the governor valve provides an annular groove 220 between the land I8 and a. third land 222 adjacent the increased pitch portion 38. An axial bore 224 and a cross port 226 opens the channel to the outer end of the governor valve, such that when the increased pitch port 38 is exposed to drain flow therefrom is restricted to that of a quantity that will prevent hunting or speed variation from the adjusted speed level. Thus, in drain from the chamber 46 thru the port 38 the hydraulic iiuid must pass thru the restricted port 226 and thence thru the axial bore 224, all as is more amply described and claimed in the copending application filed by me on October 8, 1945 as Ser. No. 621,004.

The operation of the disclosed system as effected by the three element pressure control valve is as follows: the constant-leak valve CLV maintains a constant leak from the increased pitch port 38 as long as the line is open to the valve with a pressure of as muchas 200 p. s. i. This leak is produced by the valve maintaining a constant pressure of 200 p. s. i. against the orice 150. In the preferred embodiment the amount of flow through this orifice at 200 p. s. i. is approximately 60 cubic inches per minute, which in the said preferred embodiment is equivalent to about i per second rate of pitch damage. The equalarea valve EAV maintains the approximate position shown in the sketch during normal operation, or during the equilibrium position as it is sometimes referred to, and controls the pump operating pressure, maintains it at a xed amount above the pressure at the increase pitch port 38. The equal area valve closes only when the gover.- nor valve GV is Wide open at one of the control ports calling for the f-ull available rate of pitch change, which happens only in extreme cases, such as during feathering and unfeathering operations. When the equal-area valve EAV closes, the line from the increase pitch port 38 to the leak valve CLV is shut off at I I8, from which -it will appear that the leak valve CLV does not interfere with the maximum rate of pitch change and flow-sensitive Vfeathering systems. The pressure relief valve RV limits the system pressure and operates only in extreme cases where the equal-area valve EAV may-be overdarnped. The amount of oifset of control land and port designated at Y in Fig. l, is large enough to supply the constant leak and maintain the required pressure against the ever present blade load tending to decrease pitch. If an overspeed occurs, the distance Y increases supplying more flow which increases the blade angle. If an underspeedv occurs, the distance Y decreases reducing the supply to the leak valve CLV whichY decreases the blade angle. Since the leak valve CLV is producing a constant leak the blade angle decreases at the rate of the difference in the constant leak and the amount of flow being supplied thru the governor GV.

The governor valve GV now becomes a true flow governor. The approximate 1 per second rate of decreased pitch is adequate to take care of normal operation in the described embodiment which includes the usual maneuvers withinthe operating range of the pursuit plane. The governor GV only throttles oil thru the increase pitch port 38 during normal operation. All reversing ow forces are removed from the governor valve and the constant pressure difference from the pump liney I4 to theincrease pitch line 42 is controlled by the lead of the spring 9 6 in the equal-aree valve EAV, which. .can bekcpt tea 6. A' fluid pressure system including a uid I tovv'orki'ng 'against Widely Varying' opposing r'ce, a fliiid pressure source, a governor valve With fluid ports izon'ecte`dA to opposite sides of said fluid motori', and automatically operfalme to distribute tl'e'pes'sure' source to the iirid n'iotor 7; A lid prssrel sisielmf inludiris afliid motor Working" against Widely Varying oppdsin'g f fza a fluidpe'ssure Source, @gsm/ern@ valve with" fluid pms om@fwoppsi sides o f Sai@ fllf' moto?? f utmatally 99614551519 distribute tljie prssinfe source to thi fluidmotor fQ hldne the. fudwiff iatiyend' fOr operating'l the lipid i'riotor"l in opposit-directions, @ne d fsed per@ when t -eilid mibr' inebtiiebeng open to source pressure' by a predetermined arnountpresv'siire cdfntifol means including a' constant'le'ak orifl'e, an d a valve for oontroll'- iris the 119W 0f fud' frfm iheiorie t0 match the flow frorr1` 'rsaid gov'rnoijport, said 'or'ric'ecne t r1 vali/e includingr a pressure reducingV element hidielcalli" Operated i0 rsirciflow t0 the Sei@ orifice` upon increase ofpr'e's'sure, an equal area Valve providing apair of 4spaced lands andenposed faces exposed tov source pressure andino pressure of the said governor port; a' port and passage controlled by each land, one o f said port passage being'opened to Adrain upon*I undue rise f' Piip. pressure the other Portieri# rias?- sage c nne'-ztin'g the pressure reducing element with the'said'l governor port and adapted to be at I c'ea'st"partially closed byoneof saidflands upon i' re'a'sei pressureat thesaid governor port, said equal areayalvfvoperating upon` decrease Q goyernorport openirtg4 to increase the' uid oilv througfnsaidlali ori'cie. Y Y

8. In a u'id 1;:res'sure1-system,` a pressure contro1 nit for r'nant'ainingr a pressure'p'otential in th'-systeni o f greaterl magnitude than' that deinnded for' Work.v devies'operable by the system, said control unit comprising a v alve contrlld leak o rice, a pressure controlling Valve determining theinow' tojthe'vaive controlled leak orie and having;v a rst area exposed to4 the sue'pijessiire and adapted upon predetermined rise thereof to reliii the sfdr prefssnreband havingr a second area of sad'f'li ppsig the said first area and exposed to the pressure delivered to the work device whereby to oppose the relief of said source pressure, said valve controlled leak orifice having a throttling valve controlling flow to the orifice, a pressure supply passage for the throttling valve, and means responding to an increase of pressure on the said second area of the pressure controlling valve for interrupting flow pressure supply to said throttle valve.

9. In a fluid pressure system for actuating a fluid pressure motor to adjust the pitch of blades on aircraft propellers, through a wide range of angles, comprising in combination, a source ol? fluid pressure for application to said uid pressure motor, a flow governor for directing the pressure source to the fluid pressure motor for holding the motor inactive and for actuating the motor in opposite directions, said governor having a pair of spaced ports connected to opposite sides of said motor and one of which ports is partially open to source pressure upon inactive status of said motor, valve means for maintaining a constant pressure drop across the said one governor port, and means providing a constant leak of predetermined magnitude from said governor port, and subject to the control of said valve said last mentioned valve having opposed equal areas subjected to the source pressure and to the pressure at the partially open governor port, a spring assisting the pressure at said governor port for moving said valve in opposition to the source pressure, and a port controlled by the movement of said valve for reducing the flow to said constant leak as the pressure at the partiallyopen governor port increases.

10. In a fluid pressure system for actuating a uid pressure motor to adjust the pitch of blades on aircraft propellers, through a wide range of angles, comprising in combination, a source of fluid pressure for application to said fluid pressure motor, a flow governor for directing the pressure source to the fluid pressure motor for holding the motor inactive against lthe ever present tendency to move to decrease pitch, and for actuating the motor in opposite directions for increasing and for decreasing the pitch of the blades, said flow governor having an increase pitch port and a decrease pitch port each connected with opposite sides of said motor, a pressure control unit for controlling the potential of pressure applied to said motor and including a valve for controlling the potential of pressure at said source and varying it as needed at said governor ports, said valve having equal areas exposed to the source pressure and to the pressure at the increase pitch port of said governor and being assisted by spring means for maintaining the pressure of said source, a leak orice and a controlling valve therefor maintaining a constant leak from the increase pitch port of the governor, ow or" pressure fluid to the said control valve being under the control of the rst said valve, and a valve exposed at all times to the potential of the source pressure for limiting the potential thereof to a safe value.

11. The combination set forth in claim l, wherein the leak orifice is controlled bythe combined action of two valves7 one of which is open at all times to the pressure distributed to the iiuid motor and operates to control the flow to the other, and means whereby said one valve will upon extreme demands of now by said uid motor stop all flow to said other valve and through said orice.

A12. In a'fluid pressure system for actuating a fluid pressure motor to adjust the pitch of blades on aircraft propellers, through a Wide range of angles, comprising in combination, a source of fluid pressure for application to said fluid pressure motor, a flow governor for directing the pressure source to the fluid pressure motor for holding the motor inactive and for actuating the motor in opposite directions for increasing and for decreasing the pitch of the blades, said flow governor having a pair of spaced ports connected to opposite sides of said motor and one which ports is partially open to source pressure during inactive status of said motor, such that said governor then throttles pressure fluid through only the said one port during normal operation, a pressure control unit for controlling the potential of pressure applied to said motor and including a valve for' controlling the potential of source pressure and for varying the source pressure as needed at said governor ports, said valve having equal opposed areas, one of which is constantly exposed to the source pressure and the other area of which is constantly exposed to the pressure at said one governorport and assisted by a spring to oppose the source pressure on said one area, an orifice and pressure actuated flow control valve having a port controlled by said rst mentioned valve for matching the leak through said orifice to compensate for the flow through said one governor port.

13. In a fluid pressure system for actuating a uid pressure motor to adjust the pitch of blades on aircraft propellers, through a wide range of angles, comprisingin combination, a source of fluid pressure for application to said fluid pressure motor, a flow governor for directing the pressure source to the fluid pressure motor for holding the motor inactive and for actuating the motor inV opposite directions for increasing and for decreasing the pitch of the blades, said flow governor having a pair of spaced ports connected to opposite sides of said motor one port of which throttles uid pressure to one side of the motor while the motor is held inactive, control means maintaining a pressure differential between the source pressure and the throttled pressure at said one port, said control means including apiston and cylinder having opposite equal areas exposed on the one hand to source pressure, and on the other hand to the throttled pressure at said one governor port, a port controlled by said piston and normally eX- posed to the throttled pressure of said flow governor, means controlling the flow from said piston controlled port to provide a constant leak from the system while the said pressure differential is maintained, said controlling means in- -cluding a constant leak orifice, and a iiow control valve between the said orifice and the piston controlled port, spring means operable upon said piston to assist the throttled pressure in closing the piston controlled port when the said pressure tends to decrease.

14. The combination set forth in claim 13 wherein said flow governor includes speed sensitive means for increasing the said one governor port opening in response to overspeed to throttle more uid pressure to the uid motor for pitch increase of the blades, and means including said piston and cylinder responding to the increased throttling of fluid pressure at said one governor port for increasing the source pressure. y

15. The combination set forth in claim 13 wherein said flow governor includes means sensitive to speed for decreasing the said one governor port opening in response to under speed to throttle less uid pressure to the uid motor 5 for pitch decrease of the blades, and means including said piston and cylinder responding to decrease throttling of uid pressure at said one governor port for decreasing the source pressure, and maintaining said pressure differenl0 2,384,774

tial.

RICHARD E. MOORE.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,467,522 Amsler Sept. l1, 1923 1,972,462 Schafer Sept. 4, 1934 2,167,328 Beggs July 25, 1939 Smallpeice Sept. 11, 1945 

